I have an Apple TV 2nd Gen. Still on 4.4.3. It has never been jailbroken. I just saved the SHSH Blog through iFaith. Apple is only signing 6.0.2, currently. Last tethered jailbreak is on 5.3 throught Seas0nPass.
Since you say you saved your signatures, go ahead and right click on the 4.4.3 version in SP. The IPSW creation process should begin.
However, if your 4.4.3 is like all the ones I have worked with, you are going to get a “conflict error” during the process.
Switching to a MAC at that point is the only way that I have managed to continue. And a MAC WILL be able to handle the jailbreak successfully. However, if you only have a MAC, you most likely won’t be able to save the signatures to begin the jailbreak.
I have read on this forum where others have been able to manipulate and complete the process with a PC alone. You might do a search for that info.